Change multiple specific nodes in multiple materials (with python?)
Good news - that's relatively easy:

import bpy 

sel = bpy.context.selected_objects

for obj in sel:
    try:
        for slots in obj.material_slots:
            for nodes in slots.material.node_tree.nodes:
                if nodes.type == 'EMISSION':
                    nodes.inputs[0].default_value = (1,0,0,1) # change RGBA if needd
                    nodes.inputs[1].default_value = 100 # change strength
                    #print(nodes.label) # for testing
    except: 
        print('Something wrong with ' + obj.name) # Maybe an object not capable of having materials or empty slot


You can copy/paste this into a new text block int the Text Editor and hit Run Script with the objects that have the materials you want to modify selected.